1. Field of the Invention
This invention relates to companding arrangements, in which the signal-to-noise ratio of signals transmitted via a transmission channel is enhanced by compressing the amplitudes of the signals prior to transmission and expanding the amplitudes of the signals received from the channel.
2. Related Art
It is well known to provide a companding arrangement for the transmission of telephone signals, in particular for transmission of such signals via satellite transmission channels. A significant problem arises in such arrangements during telephone call set-up, when a 2600 Hz SF (single frequency) tone is transmitted via the channel. The presence of this tone on the channel causes the gain of the expander at the receiving end of the transmission channel to adopt a higher level than would be the case in the absence of this tone. Consequently, noise picked up on the channel at other frequencies is not properly reduced. As a result, the call originator is subjected to a relatively high noise level during call set-up.